2017 ISAKOS Biennial Congress ePoster #1114


Does Knee Hyperextension Affect Dynamic In Vivo Kinematics After Anterior Cruciate Ligament Reconstruction?

Kanto Nagai, MD, PhD, Kobe, Hyogo JAPAN
Tom Gale, MS, Pittsburgh, PA UNITED STATES
Elmar Herbst, MD, PhD, Muenster GERMANY
Yasutaka Tashiro, MD, PhD, Kitakyushu JAPAN
James J. Irrgang, PT, PhD, FAPTA, Pittsburgh, PA UNITED STATES
Scott Tashman, PhD, Pittsburgh, PA UNITED STATES
Freddie H. Fu, MD, Pittsburgh, PA UNITED STATES
William Anderst, PhD, Pittsburgh, PA UNITED STATES

University of Pittsburgh, Pittsburgh, PA, UNITED STATES

FDA Status Not Applicable


This novel study investigating the effect of knee hyperextension on dynamic in vivo kinematics using the dynamic stereo X-ray system demonstrated that knee hyperextension does not significantly affect dynamic kinematics during downhill running and level walking after anatomic anterior cruciate ligament reconstruction.



There is no consensus on whether knee hyperextension affects postoperative outcome after anterior cruciate ligament reconstruction (ACL-R). One study suggests that knee hyperextension adversely affects postoperative clinical outcomes such as KT-2000 measurement, however others indicate no relationship between knee hyperextension and clinical outcome. A limitation of these previous studies is that they evaluated only static joint laxity. The purpose of the present study was to evaluate the effect of dynamic hyperextension on postoperative dynamic in vivo kinematics. It was hypothesized that patients with a high degree of knee hyperextension would have larger ranges of anterior translation and internal-external rotation during dynamic activities compared to the patients who have less hyperextension.


Forty-one patients (22±8 y.o., 27 males / 14 females) underwent unilateral ACL-R. According to the maximum extension angle of the contralateral knee during gait using dynamic stereo X-ray (DSX) images, subjects were divided into 2 groups at the median value (4.7°): Hyperextension group (n = 21, knee extension: 7.8±2.2°), and Normal extension group (n = 20, knee extension: 2.4±2.0°). Six and twenty-four months after ACL-R, subjects performed level gait and downhill running on a treadmill while DSX images were acquired at 100Hz (gait) or 150Hz (running). Tibiofemoral motion was determined from DSX images using a previously validated model-based tracking process, and tibiofemoral translations/rotations were calculated. The side-to-side differences (SSD) of range of tibiofemoral translations/rotations and the change in range of motion over time from 6 months to 24 months were also calculated. Results were analyzed using 2-way repeated-measures ANOVA, and range SSD and the change over time were analyzed using student t-test (P < 0.05).


The affected knee was significantly more extended in Hyperextension group than in Normal extension group at 6 months (3.9±4.7° vs -0.5±5.3°, P = 0.007) and 24 months (4.6±3.3° vs 0.3±4.8°, P = 0.002) after surgery. Regarding the kinematics of affected knees, there was no significant difference of anterior translation and internal rotation between 2 groups after surgery. Even in SSD, there was no significant difference between 2 groups. The change of range of internal rotation over time during running was significantly larger in Hyperextension group than in Normal extension group (2.5±3.1° vs -0.1±3.2°, P = 0.018). The result of SSD suggests internal tibial rotation range decreases over time in ACL reconstructed knee compared to the contralateral knee.


The main finding of this study was that there were no significant differences between 2 groups except the change in the range of internal rotation over time during running. However, the result of SSD indicated the range of internal rotation in affected knees decreased compared to contralateral knees in both groups. Therefore, even with a positive correlation of knee hyperextension and the change over time of internal rotation, rotational laxity decreased in both groups after surgery. Although knee hyperextension was introduced to be a risk factor for poor outcome, the results of this study do not show significant influence of knee hyperextension on the functional outcome after ACL-R.